Referring to FIG. 1 of the drawings, the reference numeral 100 generally designates a conventional DISPLAYPORT™ system that that includes a switch. DISPLAYPORT™ is a trademark of the Video Electronics Standards Association (920 Hillview Court, Suite 140, Milpital Calif. 95035), and refers to a video communication standard, specifically versions 1.1a and 1.2 (which are hereby incorporated by reference for all purposes). According to versions 1.1a and 1.2 of DISPLAYPORT™ standard, communications between a sourcing circuit 102 and a sinking circuit 104 are performed across three channels: a main channel 110, an auxiliary channel 111, and a hot plug detect or HPD channel 112. The main channel 110 is a unidirectional communication channel from the sourcing circuit 102 to the sinking circuit 104. The HPD channel is a unidirectional communication channel from the sinking circuit 104 to the sourcing circuit 102, and the auxiliary channel 111 is bi-directional.
For the auxiliary channel 111, which provides differential signals AUXM and AUXP, versions 1.1a and 1.2 of the DISPLAYPORT™ standard dictate sets of components that are to be used to couple the sourcing circuit 102, the switch 132, and the sinking circuit 104 together. Capacitors C1 and C2 (which have a capacitance between about 75 nF to about 200 nF) are used between the souring circuit 102 and switch 132. Voltage dividers (resistors R1/R2 and resistors R3/R4) are coupled across cables 106 and 108 (respectively) between a voltage source VDD and ground. Generally, resistors R1 and R3 each have a resistance of about 100 kΩ, and resistors R2 and R4 each have a resistance of about 1MΩ. Additionally, capacitors C1 and C2 (which also have capacitances between about 75 nF and about 200 nF) are provided between cables 106 and 108 (respectively) and sinking circuit 104.
In operation, the switch 132 can enable and disable communications between the sourcing circuit 102 and sinking circuit 104. Typically, switch 132 is a multiplexer with multiple sourcing and/or sinking circuits; for simplicity sake, however, only one sinking circuit 104 and one sourcing circuit 106 are shown. Within switch 132, there are terminals or pins that couple the main, auxiliary, and HPD channels of system 100, but, for simplicity sake, pins or terminals 116, 118, 120, 122, 124, 126, 128, and 130 are shown. Generally, to couple and decouple, sourcing circuit 102 from sinking circuit 104, controller provides an enable or control signal EN to switches S1 and S2 (which are generally CMOS passgates). Some problems that arise with this arrangement, however, are link establishment errors. When controller 114 activates switches S1 and S2, capacitors C1 and C2 begin charging, but to determine whether there is a link between sourcing circuit 102 and sinking circuit 104, the sinking circuit 104 measures the voltages on the auxiliary channel 111. As a result of the charging and depending on the starting potentials or voltages of capacitors C1 and C2, the voltages on the auxiliary channel 111 can be outside of an expected range, which means that the sinking circuit 104 may not assert the HPD channel 112 or may incorrectly de-assert the HPD channel 112.
Therefore, there is a need for an improved DISPLAYPORT™ switch.
Some other examples of conventional circuits are: U.S. Pat. Nos. 7,382,153; 7,679,395; U.S. Patent Pre-Grant Publ. No. 2008/0024160; U.S. Patent Pre-Grant Publ. No. 2010/0066410; PCT Publ. No. WO2003034383; and PCT Publ. No. 2003034390.